In astronomical calculations we have to account for leap seconds. Since 1972, the SI unit for the second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.
That's a mouthful, but this definition and chosen number of cycles is no accident. Oscillations of the caesium-133 atom are at the heart of how atomic clocks maintain time and the 9,192,631,770 oscillations was chosen to make atomic time, known as TAI, to be as close as possible to the historical second of observed solar time known as UT1.
The Earth's rotation speed is not constant and measurably changes very slightly over time mainly because of the slowing down of the Earth's rotation due to tidal friction with the Moon.
A body with the quirky sounding name of the Earth Rotation Service in Paris keeps track of the difference between atomic time (TAI) and solar time (UT1). They publish the time difference every few days, typically in the order of tens of milliseconds. The official world time keeping standard is UTC. It ticks at the frequency of atomic time but is adjusted when the need arises to stay within ±0.9 seconds of solar time, UT1. So now and then we insert leap seconds into the world's time keeping, literally a 61st second to a minute.
Now in a paper published in Nature on 27th March 2024, researchers have shown that after accounting for other phenomena, such as the changes in the Earth's molten core, that another factor in the accounting is due to climate change. The melting polar icecaps is causing the angular velocity of the Earth to decrease rapidly.
It's not about to change day to day life for anyone soon. But still pretty screwed up a notion that we burnt so much fossil fuels in the period starting with the Industrial Revolution that we managed to measurably change the Earth's rotational velocity.
Link to paper, "A global timekeeping problem postponed by global warming",
by Duncan Carr Agnew Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA.
https://www.nature.com/articles/s415...uXCBtEF1oj-aJi